Manufacturing method of fin unit

ABSTRACT

In a manufacturing method of a fin unit for a heat sink for dissipating a heat from a heat source, the fin unit includes a plurality of fins radially arranged about its center axis, and a fin supporting portion connecting inner ends of the fins and supporting the fins. First, metal is heated. The heated metal is extruded and/or drawn through a die to obtain a metal body. One of the die and the metal body obtained through the die is rotated relative to the other about a center axis of a die hole of the die. The metal body is then cut, thereby obtaining the fin unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fin unit for a heat sink which dissipates heat transferred from a heat source to the outside. The present invention also relates to a method for manufacturing the fin unit, and a cooling device including the fin unit.

2. Description of the Related Art

CPUs (Central Processing Units) incorporated in personal computers or servers are used with cooling devices for cooling the CPUs. The cooling device can prevent lowering of the performance of the CPU and electronic components near the CPU. An exemplary CPU cooling device is a heat sink. The heat sink includes a base portion which is in contact with the CPU via thermal grease or the like and has a central axis, and a plurality of fins radially extending from the base portion and capable of dissipating heat transferred from the CPU. The heat sink is often used together with a fan for delivering air arranged on a different surface of the base portion from a surface which is in direct or indirect contact with the CPU.

The heat generated by CPUs has been increasing with improvement of the performance of the CPUs. Thus, in the market, it is demanded that the heat sink have an improved cooling performance (heat dissipating performance). One solution is to arrange each fin at an angle relative to the central axis of the heat sink. This arrangement can increase the total surface area of the fins, i.e., an area which contributes to dissipation of the heat from the CPU to the outside, and therefore improve the cooling performance of the heat sink, without increasing the entire size of the heat sink or the number of the fins.

However, in order to arrange each fin at an angle relative to the central axis, two or more complicated additional steps, e.g., cutting or drawing are usually required after the heat sink is formed or molded. For this reason, manufacturing of the heat sink having inclined fins takes a large amount of time and cost, and therefore mass production of the heat sink is difficult.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodiments of the present invention provide a manufacturing method of a fin unit for use in a heat sink for dissipating heat from a heat source. The fin unit preferably includes a plurality of fins arranged about its center axis and a fin supporting portion connecting radially inner ends of the fins and supporting fins. The manufacturing method preferably includes: a) heating metal; b) extruding and/or drawing the metal from a die having a die hole to obtain a metal body, the die hole being shaped to correspond to the fins and the fin supporting portion; c) rotating at least one of the metal body and the die relative to the other about a center axis of the die hole; and d) cutting the metal body to obtain the fin unit. The steps b) and c) are preferably carried out in parallel.

According to another preferred embodiment of the present invention, a fin unit manufactured by the aforementioned manufacturing method is provided. Each of the fins preferably include an inner portion connected to an outer peripheral surface of the fin supporting portion, and a plurality of outer portions extending radially outward from a radially outer end of the inner portion. The inner portion is preferably defined by a single thin plate-shaped member. Each of the outer portions is preferably defined by a single thin plate-shaped member. The outer portions preferably overlap each other in a circumferential direction of the fin unit.

According to still another preferred embodiment of the present invention, a cooling device for cooling a heat source by dissipating heat transferred from the heat source is provided. The cooling device preferably includes a heat sink including the aforementioned fin unit, and a fan arranged on one axial side of the fin unit. The fan delivers air to the heat sink.

Other features, elements, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a cooling device according to a first preferred embodiment of the present invention.

FIG. 2 is a side view of the cooling device according to the first preferred embodiment of the present invention.

FIG. 3 is a plan view of a heat sink of the cooling device of the first preferred embodiment of the present invention.

FIG. 4 is a side view of the heat sink according to the first preferred embodiment of the present invention.

FIG. 5 is a flowchart for manufacturing a fin unit according to the first preferred embodiment of the present invention.

FIG. 6 is a perspective view of a die used in the heat sink according to the first preferred embodiment of the present invention.

FIG. 7 is a perspective view of the heat sink during manufacture in the first preferred embodiment of the present invention.

FIG. 8 is an enlarged view of an outer side surface of a heat sink according to a second preferred embodiment of the present invention.

FIG. 9 is an enlarged view of an outer side surface of the heat sink according to the first preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 through 9, preferred embodiments of the present invention will be described in detail. It should be noted that in the explanation of the present invention, when positional relationships among and orientations of the different components are described as being up/down or left/right, ultimately positional relationships and orientations that are in the drawings are indicated; positional relationships among and orientations of the components once having been assembled into an actual device are not indicated. Additionally, in the following description, an axial direction indicates a direction substantially parallel to a center axis, and a radial direction indicates a direction substantially perpendicular to the center axis.

First Preferred Embodiment

FIG. 1 is a perspective view of a cooling device 1 according to a first preferred embodiment of the present invention. FIG. 2 is a side view of the cooling device 1. The cooling device 1 is a heat sink fan, i.e., an assembly of a heat sink 2 and a fan 3 for delivering air to the heat sink 2 in the present preferred embodiment. The cooling device 1 is arranged adjacent to or near a heat source, e.g., a CPU in an electronic device such as a personal computer or a server, and dissipates heat transferred from the heat source through the heat sink 2 to the outside, thereby cooling the heat source.

Referring to FIGS. 1 and 2, the cooling device 1 preferably includes the heat sink 2 having a central axis J1 for dissipating the heat from the heat source to the outside, and the fan 3 for delivering air to the heat sink 2 so as to cool the heat sink 2. The fan 3 is preferably an axial fan having a rotation axis (central axis) coaxially arranged on the central axis J1 of the heat sink 2, and delivers air from one side in an axial direction to the other side, i.e., a side opposite to the heat sink 2. Please note that the axial direction is substantially parallel to the central axis J1. The fan 3 is secured to the heat sink 2, for example, with an attaching portion 4. A CPU 9 as an exemplary heat source mounted on a circuit board such as a motherboard is in contact with a surface of the heat sink 2 opposite to the fan 3 in the axial direction, as shown in FIG. 2. The cooling device 1 is preferably secured to the circuit board with at least one fixing pin 5.

In the following description, the fan 3 side and the heat sink 2 side in the axial direction are referred to as an upper side and a lower side, respectively. However, it is not necessary that the central axis J1 be parallel to the direction of gravity. In addition, a direction substantially perpendicular to the central axis J1 is referred to as a radial direction.

FIGS. 3 and 4 are a plan view and a side view of the heat sink 2. More specifically, FIGS. 3 and 4 show the heat sink 2 when viewed along the axial direction and the radial direction, respectively. Referring to FIGS. 3 and 4, the heat sink 2 includes a plurality of fins 22 arranged about the central axis J1 and extending away from the central axis J1, i.e., outward in the radial direction. Each fin 22 is preferably in the form of a thin plate, for example. The fins 22 are connected at their radially inner ends to a fin supporting portion 23 which is preferably hollow and approximately cylindrical. Inside the fin supporting portion 23 is arranged a core 24 preferably in the form of an approximately circular cylinder. As shown in FIG. 4, an axially lower end portion of the core 24 projects downward from lower ends of the fins 22 and a lower end of the fin supporting portion 23 in the axial direction. A bottom surface of the core 24, i.e., an axially lower surface of the lower end portion thereof is in contact with the CPU 9 (see FIG. 2) with thermal grease or the like arranged therebetween, for example.

As shown in FIGS. 3 and 4, a clip 25 which is preferably made of metal is attached to the lower end portion of the core 24. Exemplary materials of the clip 5 are stainless steel, aluminum, and aluminum alloy. The clip 25 includes a clip body 251 and four clip legs 252, for example. The clip body 251 has a through hole having a diameter approximately the same as that of the lower end portion of the core 24. After the lower end of the core 24 is inserted into the through hole of the clip 25, the clip 25 is fixed to the core 24 by crimping, for example. The four clip legs 252 are arranged around the central axis J1 and extend from the clip body 251 away from the central axis J1. Each clip leg 252 has a through hole 253 at its radially outer end portion, into which the fixing pin 5 is inserted. The clip 25 supports the fixing pins 5 (see FIGS. 1 and 2) via the through holes 253. As described above, the fixing pins 5 are used for fixing the cooling device 1 onto the circuit board or the like.

In the present preferred embodiment, the fins 22 and the fin supporting portion 23 are preferably formed integrally with each other from aluminum or aluminum alloy, for example. The core 24 is preferably made of copper, for example. However, the materials of the fins 22, the fin supporting portion 23, and the core 24 are not limited to the above. It is preferable that these materials have a high thermal conductivity.

In the following description, the fins 22 and the fin supporting portion 23 are referred to as a “fin unit 21” as a whole.

Referring to FIG. 3, when the fin unit 21 is viewed along the central axis J1, an outer shape of the fin unit 21, which is defined by the radially outer ends of the fins 22, is preferably approximately circular in the present preferred embodiment. Moreover, the fin unit 21 preferably includes flat portions 212 on the outer side surface thereof. When the fin unit 21 is viewed along the center axis J1, the flat portion 212 is a straight portion on the outer contour of the fin unit 21. The flat portions 212 are arranged about the central axis J1 at approximately 90-degree intervals in the present preferred embodiment. That is, two of the flat portions 212 are opposite to each other and the other two are opposite to each other, as shown in FIG. 4. Among the four flat portions 212, each of at least two flat portions 212 which are opposite to each other is provided with a groove 213 extending substantially perpendicular to the central axis J1. When engagement portions 441 of the attaching portions 4 of the fan 3 and the grooves 213 engage with each other, as shown in FIGS. 1 and 2, the fan 3 and the heat sink 2 are fixed to each other.

Returning to FIG. 3, each fin 22 of the fin unit 21 extends away from the central axis J1, i.e., outward in the radial direction, such that a distance between circumferentially adjacent fins 22 is different from or equal to each other as the fins 22 extend outward in the radial direction. Moreover, each fin 22 is preferably curved in a clockwise direction when viewed along the central axis J1. In other words, when the heat sink 2 is viewed along the central axis J1, each fin 22 is located ahead of the center of the line which connects its radially inner and outer ends to each other.

Each fin 22 includes an inner portion 221 preferably defined by a single thin plate and an outer portion 222 preferably defined by two or more thin plates, for example. In the present preferred embodiment, the outer portion 222 is defined by two thin plates. The inner portion 221 is connected at its radially inner end to the outer periphery of the fin supporting portion 23. The outer portions 222 extend from the radially outer end of the inner portion 221 outward in the radial direction, and are arranged in such a manner that two thin plates of the outer portion 222 circumferentially overlap one another. In the present preferred embodiment, the radially outer end of the inner portion 221 of each fin 22 is located at approximately the center of that fin 22 in the radial direction.

In the fin unit 21, each fin 22 has two opposing surfaces 223 and 224 which slant with respect to the axial direction, as shown in FIG. 4. When the heat sink 2 is viewed along the axial direction, a direction from a top edge (axially upper end) 225 of each fin 22 toward a bottom edge (axially lower end) 226 thereof on a radially outer edge thereof extends clockwise, as shown in FIG. 3. In other words, a plane normal to each of the surfaces 223 and 224 is not parallel to a plane substantially perpendicular to the center axis J1 of the fin unit 21. In the circumferential direction, the direction from the top edge 225 to the bottom edge 226 of each fin 22 is approximately parallel to an airflow delivered from the fan 3.

On the outer side surface 211 of the fin unit 21, except for the flat portion 212, an angle of the outer edge of each fin 22, as shown in FIG. 4, with respect to the axial direction is preferably in a range from approximately 10 degrees to approximately 50 degrees, more preferably from approximately 20 degrees to approximately 40 degrees. In the present preferred embodiment, the angle is approximately 25 degrees, for example.

As described above, the fin unit 21 of the present preferred embodiment includes the aforementioned fins 22 and the fin supporting portion 23. Thus, the surface area of the fins 22 (i.e., the area contributing to dissipation of the heat transferred from the CPU 9 to the outside) can be increased without increasing the entire size of the fin unit 21. Accordingly, the heat transferred from the CPU 9 to the heat sink 2 can be more easily dissipated to the outside and the cooling performance of the heat sink 2 can be improved.

In addition, the aforementioned structure of the fin unit 21 can eliminate the necessity of providing excessively thin fins 22 in order to increase the number of the fins 22 and in turn increase the total surface area of the fins 22. That is, the total surface area of the fins 22 can be increased while the strength of each fin 22 is kept at a sufficient level. This results in a further improvement in the cooling performance of the heat sink 2.

Moreover, it is not necessary to excessively increase the number of the fins 22. Thus, a die or mold (i.e., a die 8 described below) used for manufacturing the heat sink 2 does not need to have an excessively high dimensional precision. This means that the time and cost required for manufacturing the die or mold can be reduced. Accordingly, the time and cost for mass-production of the heat sink 2 can be reduced.

In the present preferred embodiment, the angle between the outer edge of each fin 22 and the center axis J1 preferably is approximately 10 degrees or more (more preferably, approximately 20 degrees or more), as described above. Thus, the total surface area of the fins 22 (i.e., the area contributing to dissipation of the heat transferred to the CPU 9 to the outside) can be further increased, thereby further improving the cooling performance of the heat sink 2 and the cooling device 1. On the other hand, since the angle between the outer edge of each fin 22 and the center axis J1 preferably is approximately 50 degrees or less (preferably, approximately 40 degrees or less), the fins 22 can be arranged approximately parallel to a direction of an airflow delivered by the fan 3 in accordance with a possible angle of each of the blades 324 of the impeller 322. As a result, a pressure loss of the airflow at the heat sink 2 can be reduced, enabling the airflow to draw more heat away from the heat sink 2, thus further improving the cooling performance of the cooling device 1.

Next, the fan 3 is described. The fan 3 arranged axially above the heat sink 2 as shown in FIGS. 1 and 2 includes a stator portion 31 and a rotor portion 32.

The stator portion 31 preferably includes a base portion 311, an armature (not shown), and a bearing unit (not shown). In the present preferred embodiment, the base portion 311 is approximately circular about the center axis J1, for example. In this case, the diameter of the base portion 311 is substantially the same as the diameter of the core 24 of the heat sink 2. The base portion 311 is preferably fixed to the heat sink 2 via the attaching portion 4. The armature is fixed to the base portion 311 to be opposite to the inner side surface of the rotor portion 32. The armature is electrically connected to a circuit board having at least one circuit which controls the rotation of the impeller 322 by controlling a current or signal supplied thereto from the outside. When a current is supplied from an external power supply (not shown) to the armature through at least one wire and the circuit board, for example, a torque which rotates the rotor portion 32 is generated between the armature and the rotor portion 32. The bearing unit supports the rotor portion 32 in a rotatable manner. Exemplary bearing units are a ball bearing, a bearing including a component made of sintered material impregnated with lubricant, and a hydrodynamic pressure bearing.

The rotor portion 32 is arranged axially below the base portion 311, i.e., on the heat-sink 2 side of the base portion 311. The rotor portion 32 is supported in a rotatable manner relative to the bearing unit of the stator portion 31. The rotor portion 32 includes the impeller 322 preferably made of resin or plastic, for example, and a field-generating magnet. The impeller 322 includes a hollow hub 323 and a plurality of blades 324 which are secured to the outer side surface of the hub 323 and radially extend therefrom. In the present preferred embodiment, the hub 323 is approximately cylindrical and centered about the center axis J1, is open at at least a lower end, and has substantially the same diameter as that of the base portion 311.

The field-generating magnet is fixed to the inside of the hub 323. In the present preferred embodiment, the field-generating magnet is arranged in an approximately annular configuration about the center axis J1, for example. The field-generating magnet is arranged opposite to the armature of the stator portion 31. When a current is supplied from an external power supply to the armature, a torque is generated between the armature of the stator portion 31 and the field-generating magnet of the rotor portion 32, as described above. The thus generated torque rotates the impeller 322 about the center axis J1 in a clockwise direction in FIG. 1 in the present preferred embodiment. This rotation of the impeller 322 creates an airflow flowing from the blades 324 to the heat sink 2. In the present preferred embodiment, the hub 323 and the blades 324 are preferably formed integrally with each other from resin or plastic by injection molding, for example.

Injection molding is a method for producing a product by melting a material of the product, e.g., resin or plastic, pouring the molten material into a die or mold with a pressure applied to the material, and then cooling and solidifying the material. This method is suitable for mass-production because a product having a complicated shape can be manufactured in one processing step. The dimensional precision can be increased up to plus/minus about 0.1 mm to plus/minus about 0.05 mm by optimizing the structure of the die or mold used for injection molding and the molding conditions. The die or mold is typically defined by a fixed die (mold) piece and a movable die (mold) piece. These die (mold) pieces are combined with each other to define a single die (mold).

Returning to FIGS. 1 and 2, the attaching portion 4 of the fan 3 preferably includes a frame 41, a plurality of supports 42, a plurality of ribs 43, and a plurality of rotation limiting portions 44. In the present preferred embodiment, four supports 42, four ribs 43, and four rotation limiting portions 44 are preferably provided, for example.

The frame 41 is arranged to surround the outer periphery of the impeller 322. The supports 42 extend axially upward from the frame 41 and are arranged about the center axis J1 at regular circumferential intervals. Each rib 43 is connected to the outer periphery of the base portion 311 of the fan 3 at its one end and extends outwardly in the radial direction substantially perpendicular to the center axis J1. The other end of each rib 43 is connected to an associated one of the supports 42 so that the ribs 43 support the fan 3. The rotation limiting portions 44 extend axially from the frame 41 toward the center axis J1. An opposite end portion of the rotation limiting portion 44 of the frame 41 faces an associated one of the four flat portions 212 (see FIG. 4) of the outer side surface 211 of the fin unit 21. Referring to FIG. 1, each rotation limiting portion 44 is provided with an engagement portion 441 at its axially lower end portion. The engagement portion 441 is arranged to project inward in the radial direction and to engage with the groove 213 in the associated flat portion 212. With this engagement, the circumferential movement of the attaching portion 4 and the heat sink 2 relative to the other when an impact or the like is applied from the outside can be prevented.

Next, a preferred method of manufacturing the fin unit 21 of the heat sink 2 is described. FIG. 5 illustrates an exemplary manufacturing process of the fin unit 21. In this preferred embodiment of the present invention, a plurality of fin units 21 are preferably manufactured while being connected to one another in their axial direction, and are then separated from one another. FIG. 6 is a perspective view of a die 8 preferably used for manufacturing the fin unit 21. FIG. 7 shows the fin unit 21 during manufacture. The die 8 used in this preferred embodiment has an approximately flat plate in which a die hole 81 having a shape corresponding to the fins 22, the fin supporting portion 23, and the core 24 is provided.

First, a material of the fin unit 21 is softened by being heated to a high temperature (Step S11). In this preferred embodiment, an approximately circular cylinder of aluminum or aluminum alloy is heated to approximately 500° C. to soften the aluminum or aluminum alloy (Step S11).

Then, Step S12 is preferably carried out as follows. As shown in FIG. 7, the softened material 200 is placed in a container 80 for extrusion and is shaped into a hollow, approximately cylindrical shape, for example. The thus shaped softened material 200 is pressed by a pressing device (not shown) driven by a servo motor (not shown) against the die 8 having a shape shown in FIG. 6. A space within the shaped material 200 corresponds to a space inside the fin supporting unit 23 of the fin unit 21 shown in FIG. 3. The core 24 is then inserted into the space in the shaped material 200. The space is coaxial with a center axis J2 of the die hole 81 of the die 8 shown in FIG. 6.

The material 200 is pressed against the surface of the die 8 on one side in its axial direction parallel to the center axis J2 and is extruded through the die hole 81 from the surface of the other side of the die 8. In the example of FIG. 7, the material 200 is pressed against the left surface of the die 8 and is extruded from the right surface. In this manner, a metal body 201 is obtained which extends continuously substantially parallel to the center axis J2 of the die 8 and has portions defining a plurality of fins 22 and a portion defining the fin supporting portion 23. A space defined inside the fin supporting portion 23 has a center axis coaxial with the center axis J2 of the die hole 81.

In the following description, the portions which define the fins 22 and the portion which defines the fin supporting portion 23 are referred to as the fins 22 and the fin supporting portion 23, respectively.

Then, a supporting member 82, which is preferably in the shape of an approximately circular cylinder, for example, is inserted into the space inside the fin supporting portion 23 of the metal body 201, and connected to the metal body 201. The supporting member 82 is then moved away from the die 8 along the center axis J2 of the die 8 while being placed in the fin supporting portion 23 of the metal body 201, thereby drawing the metal body 201 from the die hole 81. Please note that the supporting member 82 is arranged with its center axis J3 substantially coincident with the center axis J2 of the die hole 81.

While the softened metal material 200 is extruded and drawn from the die 8 in the aforementioned manner, the supporting member 82 is rotated about its center axis J3. In this preferred embodiment, when the supporting member 82, the die 8, and the material 200 are viewed from the right in FIG. 7, i.e., they are viewed from the downstream side in a direction in which the metal body 201 is drawn, the supporting member 82 is rotated in a counterclockwise direction. That is, the supporting member 82 is moved from left to right in FIG. 7, while being rotated in the counterclockwise direction when viewed from the right in FIG. 7.

Due to the rotation of the supporting member 82, the metal body 201 exiting from the die 8 is rotated about the center axis J2 of the die hole 81 of the die 8 relative to the die hole 81. As a result, a plurality of fins 22 are inclined with respect to the center axis J2 of the die hole 81 (Step S12).

As described above, formation of the fins 22 and a process for inclining the respective fins 22 with respect to the center axis J2 are preferably carried out simultaneously in this preferred embodiment. Thus, it is possible to easily manufacture the fin unit 21 having the fins 22 inclined with respect to the center axis J1 of the fin unit 21.

Moreover, the rotation of one of the metal body 201 and the die 8 relative to the other is preferably achieved by rotating the metal body 201 while the die 8 is fixed. Thus, a load applied to the die 8 during this relative rotation can be reduced and control of this relative rotation can be simplified. Accordingly, the fin unit 21 of this preferred embodiment can be easily manufactured without requiring a complicated process.

The supporting member 82 is connected to a servo motor which operates at a controlled rotation speed in synchronization with the servo motor for pressing the metal 200 against the die 8. The reason for this is now described. A relationship between the rotation speed of the supporting member 82 for supporting a portion around a leading end of the metal body 201 and the rotation speed of a portion of the metal body 201 near the die 8, i.e., a relationship of the rotation speed between both axial ends of the metal body 201 is changed depending on the axial distance between the leading end of the metal body 201 and the die 8. Thus, it is necessary to control the rotation speed of the metal body 201 at both axial ends so that inclination of the fins 22 with respect to the center axis J2 is substantially the same at both axial ends of the metal body 201. For this reason, the rotation of the supporting member 82 is performed by using the servo motor and the rotation speed thereof is controlled. In this manner, it is possible to control the rotation speed of the metal body 201 near the die 8 with high precision and therefore manufacture the fin unit 21 with high precision. In addition, the fin unit 21 can be made with even higher precision by controlling a rate at which the metal body 201 is drawn from the die 8 by using another servo motor synchronized with the servo motor for rotating the supporting member 82.

Step S13 is now described. After the metal body 201 is formed and shaped by extrusion and drawing in Steps S11 and S12, the metal body 201 is cooled by, for example, air delivered by an air-blowing apparatus. The thus cooled metal body 201 is subjected to a heat treatment for improving the hardness and strength thereof. In this preferred embodiment, the metal body 201 is heated to approximately 185° C.

In the following Step S14, the metal body 201 is cooled by water, air delivered by an air-blowing apparatus, or the like. Then, the metal body 201 is cut at a plurality of points in its longitudinal direction (which is substantially parallel to the center axis J2 of the die hole 81) in such a manner that a cut plane thereof is substantially perpendicular to the longitudinal direction. In this manner, a plurality of fin units 21 (see FIG. 3) each having a plurality of fins 22 and the fin supporting portion 23 are easily and rapidly manufactured while being separated from one another.

In the above-described method, the fin units 21 are cut after the heat treatment of the heat body 201 in Steps S13 and S14. However, the order of these steps is not limited to the above. The heat treatment may be individually carried out for each of the fin units 21 after they are separated from each other. Alternatively, the heat treatment and separation of the fin units 21 may be carried out at the same time.

In the following Step S15, the outer peripheral surface 211 of each fin unit 21 obtained in Step S14 is partially cut, thereby forming flat portions 212 and grooves 213 (see FIG. 4). Then, the inner side surface of the hollow fin supporting portion 23 of each fin unit 21 is finished by CNC (computer numerical control) machining which can provide a high precision of processing, e.g., broaching. The manufacturing process of the fin unit 21 preferably ends with this step.

After the fin unit 21 is manufactured, the fin unit 21 is heated again, and the core 24 is inserted into the fin supporting portion 23 of the fin unit 21 and fixed thereto by shrink fitting, for example. In this preferred embodiment, the fin unit 21 is heated to approximately 300° C. and the core 24 in the shape of the approximately circular cylinder is inserted into and fitted to the fin supporting portion 23. Thus, the heat sink 2 is manufactured. Then, the clip 25 is secured to the lower end portion of the core 24 of the heat sink 2, as shown in FIG. 4. Additionally, the fan 3 is attached on the upper side of the heat sink 2, as shown in FIGS. 1 and 2, thereby completing the cooling device 1.

As described above, in Step S15 finishing is performed for the inner side surface of the fin supporting portion 23 of the fin unit 21 obtained by cutting the metal body 201. This finishing can improve adhesion of the inner side surface of the fin supporting portion 23 and the outer side surface of the core 24 to each other, i.e., adhesion of the fin unit 21 and the core 24 to each other. Consequently, thermal conductivity from the core 24 to the fin unit 21 is improved, resulting in the efficient transfer of heat from a heat source such as the CPU 9 to the fin unit 21. Thus, the cooling performance of the heat sink 2 can be further improved.

The fin unit 21 of this preferred embodiment is made of aluminum or aluminum alloy. Aluminum and aluminum alloy are excellent in thermal conductivity and workability, and easily available. Therefore, when the heat sink 2 is made of aluminum or aluminum alloy, heat resistance of the heat sink 2 can be reduced and the cooling performance of the heat sink 2 is improved. Moreover, the use of aluminum or aluminum alloy as the material of the heat sink 2 enables easy manufacturing of the fin unit 21 and reduces the manufacturing cost of the fin unit 21.

Second Preferred Embodiment

A fin unit of a heat sink according to a second preferred embodiment of the present invention is now described. The fin unit 21 a of the second preferred embodiment preferably has substantially the same structure as the fin unit 21 shown in FIGS. 3 and 4. In the following description, respective components of the fin unit 21 a are labeled with the same reference signs as those for the corresponding components of the fin unit 21. The fin unit 21 a of the present preferred embodiment is preferably manufactured in substantially the same manner as the fin unit 21 of the first preferred embodiment, except that while the metal body 201 is extruded and drawn from the die 8 (see FIG. 7) and rotated, the rotation speed of the metal body 201 is changed.

FIG. 8 shows the outer side surface 211 of the fin unit 21 a of the present preferred embodiment in an enlarged view. In this description, the outer side surface of the fin unit means an approximately cylindrical shape defined by the outer peripheral edges of the fins 22 along the circumferential direction. FIG. 9 shows the outer side surface 211 of the fin unit 21 of the first preferred embodiment in an enlarged view. In FIGS. 8 and 9, the outer side surface 211 in a state before the flat portions 212 (see FIGS. 1 to 4) are formed are shown for facilitating the understanding of these drawings. Moreover, the number of the fins 22 shown in FIGS. 8 and 9 is different from the actual number. Please note that the number of the fins 22 is not specifically limited.

In the manufacturing method of the present preferred embodiment, while a portion of the metal body 201 which corresponds to a single fin unit 21 a is extruded and drawn from the die 8, the rotation speed of the supporting member 82 (FIG. 7) is gradually changed such that in that portion of the metal body 201, an inclination angle of each fin 22 with respect to the center axis J2 of the die 8 (see FIG. 6) is changed along the center axis J2. More specifically, the inclination angle of each fin 22 with respect to the center axis J2 is larger in a region near the supporting member 82 (the upper portion in FIG. 8) than in a region axially apart from the supporting member 82 (the lower portion in FIG. 8). For example, the inclination angle of each fin 22 with respect to the center axis J2 of the die 8 at a radially outer edge of that fin 22 is larger than that at any portion inside the radially outer edge of that fin 22.

In other words, while attention is focused on a portion of the metal body 201 which corresponds to a single fin unit, each fin 22 is curved to be convex toward the supporting member 82 (i.e., upward in FIG. 8) on a plane obtained by connecting supporting member 82 side ends of the fins 22 (i.e., upper ends in FIG. 8) and opposite ends thereof to each other.

In the manufacturing method of the fin unit 21 a of this preferred embodiment, extrusion and drawing of the metal body 201 and rotation of the metal body 201 relative to the die hole 81 are preferably carried out simultaneously as in the first preferred embodiment. Thus, the fin unit 21 a having the fins 22 respectively inclined with respect to the center axis J1 of the fin unit 21 a can be easily manufactured.

Especially in this preferred embodiment, each fin 22 is curved with respect to the center axis J2 due to the change in the rotation speed of the metal body 201. That is, an angle formed by the outer peripheral edge of each fin 22 and the center axis J2 is varied. With this configuration of the fins 22, the surface area of the fins 22 can be increased as compared with a case where the fins 22 are not curved but are straight, thus improving the cooling performance of the heat sink. On the other hand, according to the manufacturing method of the heat sink in the first preferred embodiment, control of the rotation speed of the supporting member 82 (see FIG. 7) can be simplified. Thus, the manufacturing process can be simplified.

Although the preferred embodiments of the present invention are described above, the present invention is not limited thereto. The present invention can be implemented by varying the aforementioned preferred embodiments in various ways.

In the fin unit 21 of the first preferred embodiment, it is not always necessary that each fin 22 is inclined with respect to the center axis J1 to be approximately parallel to an airflow from the fan 3 over the entire length thereof. The effect that the airflow can enter between the fins 22 smoothly can be achieved by inclining at least an axially upper portion of each fin 22 with respect to the center axis J1 so that the portion is approximately parallel to the airflow from the fan 3. Here, the axially upper portion of each fin 22 is a fan 3 side portion of each fin 22 in the axial direction. As a result, a pressure loss of the airflow from the fan 3 at the heat sink 2 can be reduced, and the amount of heat the airflow can receive from the heat sink 2 can be increased. Thus, the cooling performance of the cooling device 1 is improved. In this case, when the outer peripheral edge of the inclined portion of each fin 22 is inclined with respect to the center axis J1 of the fin unit 21 at an angle in a range from approximately 10° to approximately 50°, more preferably approximately 20° to approximately 40°, the cooling performance of the cooling device 1 can be further improved.

In the cooling device 1 of the first preferred embodiment, it is not always necessary that the axis of rotation of the fan 3 is coincident with the center axis J1 of the fin unit 21. The axis of rotation of the fan 3 may be spaced from the center axis J1, as long as they are substantially parallel to each other.

The heat sink 2 may be provided with a recess on the axially upper end surface of the core 24. The recess may have any shape, for example, a tapered shape in which an inner diameter thereof is reduced as it moves axially downward, a shape of a polygonal column, a conical shape. In this case, it is possible to reduce the weight of the core 24 while keeping the cooling performance of the heat sink 2 at a level required by a customer, or even at a higher level. Thus, the manufacturing cost of the heat sink 2 can be reduced.

In the fin 22 of the first preferred embodiment, two or more outer portions 222 are formed radially outside the radially outer end of the inner portion 221 which is located around the center of each fin 22 when the fin 22 is viewed along the center axis J1. However, it is not always necessary that each fin 22 is divided into a plurality of outer portions at the radially outer end of the inner portion 221. In other words, each fin 22 may be defined by a single plate along its entire length with no branching portion.

Moreover, the core 24 is preferably arranged inside the fin supporting portion 23 in the first preferred embodiment. However, the core 24 may be omitted. The core 24 may be omitted if the fin supporting portion 23 is formed into an approximately cylindrical shape which is not hollow. In this case, the lower end of the fin supporting portion 23 is in contact with a heat source such as the CPU 9.

In the manufacturing method of any of the above-described preferred embodiments, it is not always necessary that the metal material 200 is heated and softened. The metal material 200 may be heated to a temperature lower than a temperature at which the material 200 is softened.

In Step S12 of the aforementioned manufacturing method, the metal material 200 is extruded from the die hole 81 of the die 8 and the extruded metal body 201 is drawn from the die hole 81 while being supported by the supporting member 82. However, the present invention is not limited thereto. Only one of the steps of extruding and drawing of the metal material 200 may be performed.

The rotation of the metal body 201 relative to the die hole 81 in Step S12 is not always achieved by rotating the metal body 201 relative to the fixed die 8. Alternatively, while the metal body 201 is extruded and/or drawn from the die 8 without being rotated, the die 8 maybe rotated about the center axis J2 thereof. Alternatively, while the metal body 201 is extruded and/or drawn from the die 8, both the metal body 201 and the die 8 may be rotated.

In the manufacturing method of the aforementioned preferred embodiments, a plurality of fin units 21 are preferably formed from a single continuous block of material 200. However, the above manufacturing method can be applied to a case where only one fin unit 21 is formed from a single continuous block of material 200. In this case, the fin unit is obtained by cutting both longitudinal ends (both axial ends) of the metal body 201 obtained from the die 8, which is continuous in the axial direction.

It is not always necessary to use aluminum or aluminum alloy as the material of the fin unit. Other metals or alloys which can be processed by extrusion and/or drawing, e.g., copper and iron may be used. Moreover, the material of the core 24 is not limited to copper, as described above. The same material as the fin unit, e.g., aluminum or aluminum alloy, may be used for the core 24. In this case, the core 24 may be integral with the fin supporting portion 23 when the fin unit is manufactured.

The heat sink of any of the above preferred embodiments is not necessarily used together with the fan 3 attached thereon to define the cooling device 1. The heat sink of any of the above preferred embodiments may be attached to a heat source by itself so as to dissipate heat transferred from the heat source.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1. A manufacturing method of a fin unit for a heat sink for dissipating heat from a heat source, the fin unit including a plurality of fins arranged about a center axis and a fin supporting portion connecting radially inner ends of the fins, the manufacturing method comprising the steps of: a) heating a metal; b) extruding and/or drawing the metal from a die having a die hole to obtain a metal body, the die hole being shaped to correspond to the fins and the fin supporting portion; c) rotating at least one of the metal body and the die relative to the other about a center axis of the die hole; d) cutting the metal body to obtain the fin unit; wherein at least a portion of each of the steps b) and c) are carried out simultaneously.
 2. The manufacturing method according to claim 1, wherein in the step c), the metal body is connected to a supporting member and the die is fixed relative to the metal body, and the metal body is rotated about the center axis of the die hole relative to the die by rotating the supporting member about the center axis of the die hole.
 3. The manufacturing method according to claim 2, wherein the supporting member is rotated by a first servo motor.
 4. The manufacturing method according to claim 3, wherein the step of extruding and/or drawing the metal from the die is performed via a second servo motor.
 5. The manufacturing method according to claim 4, wherein the first servo motor and the second servo motor are controlled in synchronization with each other to control a rate at which the metal body is obtained from the die and a rotation speed of the supporting member in accordance with a distance between a leading end of the metal body and the die.
 6. The manufacturing method according to claim 1, wherein a rotation speed of the metal body is changed to change an inclination angle of a portion of the metal body which corresponds to an outer peripheral edge of each of the fins with respect to the center axis of the die.
 7. The manufacturing method according to claim 1, wherein the metal is aluminum or aluminum alloy.
 8. The manufacturing method according to claim 1, wherein the metal body extends continuously substantially parallel to the center axis of the die, and includes a plurality of fin units each of which has the fins and the fin supporting portion and which are arranged substantially parallel to the center axis of the die.
 9. The manufacturing method according to claim 1, further comprising the step of: e) finishing an inner peripheral surface of the fin supporting portion which is hollow and obtained in step c).
 10. The manufacturing method according to claim 1, further comprising the step of: f) performing a heat treatment on the metal body or the fin unit.
 11. A fin unit manufactured by the manufacturing method according to claim
 1. 12. The fin unit according to claim 11, wherein each of the fins includes an inner portion connected to an outer peripheral surface of the fin supporting portion, and a plurality of outer portions extending radially outward from a radially outer end of the inner portion; the inner portion is defined by a single thin plate-shaped member, and each of the outer portions is defined by a single thin plate-shaped member; and the outer portions overlap each other in a circumferential direction of the fin unit.
 13. The fin unit according to claim 11, wherein each of the fins extends radially outward from the fin supporting portion and are curved in a clockwise or counterclockwise direction when viewed along the center axis.
 14. A cooling device for cooling a heat source by dissipating heat transferred from the heat source, comprising: a heat sink including the fin unit according to claim 11; and a fan arranged on one axial side of the fin unit; wherein the fan is arranged to deliver air to the heat sink.
 15. The cooling device according to claim 14, wherein a fan-side portion of each of the fins of the fin unit is inclined with respect to the center axis of the fin unit so as to be approximately parallel to an airflow from the fan.
 16. The cooling device according to claim 14, wherein an outer peripheral edge of a fan-side portion of each of the fins is inclined with respect to the center axis of the fin unit at an angle in a range from approximately 10 degrees to approximately 50 degrees. 